More than 600 people have been evacuated from central Syrian city of Homs, with aid agencies battling mortar shells and gunfire to reach stricken civilans trapped by 18 months of fighting between rebels and government forces.

Aid teams have helped 611 people to flee the besieged city since Friday, with the majority exiting on Sunday, and delivering much needed food and medical supplies to those preparing to leave or wishing to stay.

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But the evacuation has come at a cost, with the UK-based Syrian Observatory for Human Rights saying that five people were killed by mortar shells and two from gunfire in the Old City on Sunday.

Violence broke out on Saturday and threatened to altogether scupper the humanitarian access that had been eked out during peace talks in Geneva two weeks ago. The explosions and gunshots also violated a three-day ceasefire that began on Friday.

The ceasefire has been extended for another three days, the governor of Homs Talal Barzai told Al Jazeera.

Khaled Erksoussi, head of operations at the Syrian Arab Red Crescent, told Associated Press news agency that Saturday's attacks left one aid worker wounded. At least nine Red Crescent and UN vehicles were trapped in Homs for several hours, but the team managed to escape shortly before 8:00pm GMT, leaving behind two damaged lorries.

According to its Twitter feed, SARC workers were able to get 60 food parcels and 1500kg of flour inside the Old City on Sunday. Its workers also provided medical assistance and food to evacuees.

Syrian forces loyal to President Bashar al-Assad have prevented the entry of food and medical aid into parts of Homs for more than a year.

Source: Al Jazeera and agencies